5 gallon batches fine, 2.5 gallon batches - efficiency issues

Hello everyone,

I've been using BeerSmith for a while and I love it.  My only problem lately is that I've been having serious efficiency issues with my 'half size' batches.  Specifically, while I usually get around 70% mash efficiency with my 5 gallon batches, my 2.5 gallon batches have been giving me efficiencies ranging from 50-60%. 

Being that this could be an equipment/technique issue just as easily as it could be a software issue, here's a summary of my fairly basic apartment brewing system.

-10 gallon brew kettle that I position over 2 stovetop burners
-10 gallon rubbermaid converted into a MLT, complete with false bottom screen.
-I mill my own grain with a Cereal Killer grain mill, and use a feeler gauge to set the gap to ~.038.
-I also have a copper wort chiller I bought from MoreBeer, a William's Brewing oxygenation system, and other bells & whistles that aren't really relevant to my current problem which is mash efficiency.

Getting back to BeerSmith, one thing I noticed for my 2.5 gallon equipment profile as opposed to my 5 gallon equipment profile is that while both 'Brewhouse efficiency' values are set to 72%, for some reason my 5 gallon profile has an estimated mash efficiency of 78% whereas my 2.5 gallon profile has an estimated mash efficiency of 85%.

My ACTUAL mash efficiencies in my 5 gallon batches range from 70-80% as expected, whereas my ACTUAL mash efficiencies in my 2.5 gallon batches are all over the place, but typically lower in the 50-60% range like I said.

Now, at the end of the day this could be a process problem (I understand that brewing smaller batches using equipment suited to larger batches can cause issues - the last few 'driblets' of runoff that you lose in the grain bed are a more significant portion of 2.5 gallon batches than 5 gallon batches, for example). 

However, I still gotta ask why BeerSmith assumes a higher mash efficiency in my 2.5 gallon setup vs. my 5 gallon setup, particularly when the input value for BrewHouse efficiency is equal.

For now I think I'll have to plan on using significantly more than 50% grain in my half size batches to compensate for my much lower mash efficiencies, unless there are any other obvious solutions?

Thanks and cheers everyone.

-BeerBeard

Mash efficiency is the measure of sugar extraction into the kettle.
Brewhouse Efficiency is the measure of total potential sugars that make it into the fermenter.

BeerSmith doesn't dilute the potential sugar when loss to trub & chiller is entered. Instead, it assumes more extraction from the grain. More loss = more volume at the same gravity = more mash efficiency to achieve it.

Your actual mash efficiency may be related to the total volume of water in and under the mash. This can substantially dilute the enzymes and substrate. The correction for this is to extend the mash time. I suggest that you take gravity readings beginning at 45 minutes and don't recirculate until the gravity stops rising for 15 minutes. A refractometer is the most efficient device for this purpose.

Why does BeerSmith assume more extraction at smaller volumes?  I didn't follow your more loss = more volume = more mash efficiency statement.

To illustrate this, I'm going to work outside the realm of possibility. I'm just going to start with easy to remember and adjust parameters. We're going to start with a recipe for 10 gallons using 10 pounds of malt as a baseline. I've attached it below.

Double click on the grain. You'll see two fields: Potential and Yield. These two are different ways of saying the same thing. Namely, the maximum soluble potential of one pound of grain dissolved to make one gallon of wort. They are based on the potential of one pound of sucrose for one gallon of water.

The field for coarse/fine difference underneath SHOULD paly a role, but it's a red herring adjustment, so we're going to ignore it.

I'm going to set the yield to 87%, which shows a yield of 1.040. It's just a round number.

I set up an equipment profile that has 100% brewhouse efficiency, no boiloff, no shrinkage and no loss to trub. So, the starting point is showing 100% mash efficiency (1.040 est OG) AND 100% Brewhouse efficiency (1.040).

The first adjustment to make is to open the equipment profile and add 1 gallon of loss to trub. Go to the mash tab and note that the estimated volume is now 11 gallons, but the OG is still 1.040. BeerSmith has adjusted the mash efficiency to 110% to account for the increased volume (10%). The Fermentation tab still shows 10 gallons batch size and 1.040 OG.

The next adjustment is to change the batch size to 5 gallons. Everything else stays the same. The mash tab now shows 1.080, which makes sense because the same grain is now making half the wort.

But notice that the mash efficiency is now 120%. The trub loss hasn't changed because in this study, we're using "the same" pot with the same trub loss. That loss now represents a larger percentage of lost sugar because it can't become beer if it doesn't get into the fermenter.

So, the Brewhouse Efficiency has to come down for smaller batches to account for the increased percentage of lost sugars in the trub.

If we go back to the original settings (10 gallon batch, zero trub loss) and just change the Brewhouse efficiency to 75%, we get a potential OG of 1.030. Add just 1 gallon of trub, and the mash efficiency climbs to 82%. Why? because the increased volume is assumed to be at the same gravity, so it has to be created by better mash efficiency.

If we once again drop the batch size, we see a doubling of gravity, and the mash efficiency goes up again, to 90%.

So, you probably have noticed that your mash efficiency stays pretty constant. This can ONLY mean that the Brewhouse Efficiency must need to be adjusted downward to show the correct gravity, volume and mash efficiency.

To get a 75% mash efficiency at 10 gallons with 1 gallon loss to trub, the Brewhouse efficiency needs to be about 68%.

By contrast, to get a 75% mash efficiency at 5 gallons with 1 gallon loss to trub, the Brewhouse efficiency falls to about 62%.

Brewfun - Your post has got to be one of the most helpful posts I've read in some time.  I have been struggling with why my efficiencies have dropped since increasing the loss to trub and boiloff settings after purchasing a new kettle.  I never noticed that my estimated mash efficiencies were up in the high 90s.  Thanks for pointing this out.  I went back and reviewed the mash efficiencies I was actually getting under the new equipment profile, and they were consistent with the mash efficiencies I was getting under the old profile.  Bingo!  It all makes sense now. You're a lifesaver.

Thanks,

You're welcome!  I appreciate hearing that it helped.